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Plywood is composed of odd number of thin layer of wood piles bonded together with a rigid adhesive. Thus manufactured Plywood Boards are extensively used for several industrial purposes. Mehta Wood Industry is one of Wholesale Packing Plywood Manufacturers in India. The Plywood Boards supplied by us are remarkable for their stiffness as well as strength. They are extensively as well as effectively used for construction of doors, cabinets, panels and so on. The most remarkable aspect about our plywood boards is that they are light weighted and very durable. And when it comes to the wholesale plywood sheet suppliers in the market, we are the name to reckon with. Besides, we are one of the largest solid plywood manufacturers in the country.
Plywood is a versatile wood product, which makes it in great demand by contractors. America alone uses more than sixteen thousand million square feet every year which is meaningless until it is compared to a twelve-foot-wide pathway stretching from earth to beyond the moon. Plywood is a building material made from layers of thinly sliced wood, which is glued together. Each layer called a ply is arranged so that the direction of the wood fibers or grain is placed at right angles to the layer next to it & make Plywood & Veneer Production.
This placement of the layers equalizes a panel’s strength and prevents splitting. Plywood is usually made of three plies, but five, seven, nine, or even more plies may be used in some situations. The most common sizes of plywood are 4 feet wide and eight feet long and ¼ to ¾ inches thick. The dimensions and thickness can be different according to how the plywood is to be used. Two types of plywood are interior and exterior. Interior plywood is made with glues that are moisture-resistant. This means that the glue in the interior of the plywood has a limited resistance to water. On the other hand exterior plywood is designed to better withstand conditions resulting from moisture and humidity. This means that the adhesive of exterior plywood is capable of withstanding a certain amount of moisture before it starts to decay. Exterior plywood is also made with waterproof glues. The manufacturing process of making plywood consists of several steps. These steps include : Selecting the log, Stripping the bark, Peeling the log, Making a continuous ribbon of wood, Cutting and stacking, Gluing, Pressing, and Trimming, Sanding, and Finishing the wood.
Why Make Plywood : Timber is around thirty times weaker across the grain than along its grain direction. This is obvious when we split wood with an axe. Thus by bonding adjacent timber veneers at right angles using a rigid adhesive as happens in the cross laminated construction of plywood, we utilise this superior strength and stiffness along the grain to overcome this weakness. Put another way, plywood has no natural line of cleavage. Plywood maintains the integrity of the timber and finds a huge range of applications which utilise the enhanced properties mentioned below.
Dimensional Stability : Timber expands and contracts across its grain as it takes in and loses moisture to the atmosphere. The change in length along the grain due to changes in moisture is 1/100 of that across the grain. This factor, combined with timber’s much greater strength along the grain, in the cross laminated structure of plywood locks up this movement. This gives plywood excellent two way dimensional stability which is advantageous in applications such as large areas of flooring or concrete formwork.
Strength And Stiffness/Weight Ratio : The cross laminated structure further enhances timber’s high strength and stiffness to weight which is a major reason plywood is used in such applications as formwork, flooring, fabricated beams, road transport and materials handling. For example, the strength to weight ratio of F11 structural plywood is close to 4½ times the ratio for Grade 250 steel.
Split Resistance : The cross lamination controls any tendency for splitting along the grain and thus enables nailing or screwing very close to all panel edges. Additionally, plywood is highly resistant to edge damage when compared to other panels. These two properties combine to make plywood a rugged building panel.
Panel Shear or Shear Through Thickness Capacity : Panel shear capacity is the ability to resist loads in the plane of the panel. As plywood’s cross laminated structure prevents the tendency to split along the grain it has double the panel shear capacity of timber. This makes plywood an excellent material for bracing for residential wall framing, floor, wall and roof diaphragms, the webs in box, C or I-beams, and for gusset plates in timber portal frames.
Resistance To Concentrated Loads : Plywood’s cross lamination spreads loads sideways and gives plywood its excellent ability to carry high concentrated and impact loads that would break or shatter many other materials.
Resilience, Impact And Fatigue Resistance : As the structure of the timber is maintained and the fibres not smashed during plywood manufacture these closely related properties are all derived from the parent wood. Timber has high short term load capacity, and is able to elastically spring back or recover its original shape after shock or impact loads. Plywood’s structure further enhances this high resilience and impact resistance. Plywood, being an organic cellulose material is not subject to the fatigue failure of crystalline materials, e.g. metals and plastics. Plywood thus can endure cyclic stresses much longer than these crystalline materials which means it is able to maintain its strength under repeated loading.
Thermal Insulation With Low Thermal Mass : Plywood, like its parent wood is a good thermal insulator plus it has a relatively low specific heat when compared to other building materials. These two properties can be utilised for thermally efficient floor, wall and roof construction.
Chemical Resistance : Plywood reacts to chemical exposure much the same as wood, in that it has reasonable resistance to acid (pH 2) and alkaline (pH 10) conditions. Thus it can safely be used in most areas exposed to chemicals, for example in heated indoor swimming pool enclosures. Plywood performs very well in seaside applications under exposure to salt mist, thus preservative treated plywood makes an excellent external cladding for beachside housing. The preservation being to protect the wood from fungal attack. In fact, plywood cladding has a low vapour permeance thus it is also a good vapour barrier.
Sound Reflectance : Plywood’s ability to reflect sound is used to reflect traffic noise from highways, and in theatres as a lining to enhance the room acoustics.
Workability : Plywood can be worked with the same ease as timber. Sawing, gluing, nailing or screwing pose no problems
Aesthetics : Timber and plywood look great!
Plywood Is Timber Made Better!
Timber is a precious resource and the fact low quality, fast-grown timber can be used for the manufacture of plywoods means maximum value adding. Plywood from plantation timber, is an environmentally correct material. The modern structural plywoods have all the above advantages and can be used both aesthetically and structurally.
Log Preparation : The logs are first ‘debarked’ after delivery from the plantation. This is achieved by a machine which mechanically scrapes the bark from the log. It is good practice to ‘condition’ the log before peeling. This can be achieved by water sprays, immersing in cold or heated water, or by steam treatment. This ensures the log is at a high and consistent moisture content throughout which facilitates peeling and helps yield smooth veneer with less tendency to split or tear. Heating the log softens the timber fibres and further improves veneer quality and yield. Before peeling the logs need to be ‘docked’ or cut into ‘blocks’ or ‘billets’ around 100mm longer than the finished plywood panel, i.e. usually 2½ metres. The log is now ready to be conveyed into the plant for peeling.
Peeling : The initial process in peeling is to load and centre the peeler block in the spindles of the veneer lathe. The peeler block must be centred with the axis of the log along the centre line of the lathe spindles to obtain maximum veneer recovery. This can be done manually, but is best achieved by an ‘x - y charging system’. This system uses a laser scanner to measure the block three dimensionally and uses a computer to calculate the largest perfect cylinder within the block. The system then locates the block in the best position for the lathe. The lathe effectively rotates the block against the lathe blade or ‘knife’ which peels the veneer off in long continuous veneer ribbon of consistent thickness.
Clipping : The ribbon of veneer passes from the lathe through manual or automated clipping machines which cut or ‘clip’ the veneer to size, or into smaller strips if defective material has been removed. In some mills producing high quality thin veneer, clipping is done after the continuous ribbons of veneer have been dried so as to maximise the number of full sheets obtained.
Drying : The wet veneer is fed through a drier to reduce its moisture content to about 8% from the ‘green’ moisture content of between 40-140%. The optimum moisture content for gluing depends on the species and density of the veneer, and the adhesive and gluing procedures being used. In mechanical driers the veneer is conveyed through a long chamber in which hot air is circulated Driers can have one, or as many as five separate conveyors, one above the other. The drying time is regulated by adjusting the speed of the conveyors and/or the temperature of the hot air.
Jointing or Veneer Repair : Small strips of veneer may be jointed into full size sheets by edge gluing, stitching or using perforated tape. Open defects may be repaired by using plugs to upgrade the veneer.
Crossbands : The core veneers that run across the panels at right angles to the face veneers are termed ‘crossbands’. In a 2400mm x 1200mm panel the crossbands can be produced by a smaller lathe, or by cutting full sheets of veneer into two.
Grading : The dried, clipped and perhaps jointed or repaired veneers are graded in preparation for use in plywood manufacture.
Sliced Veneer : In general plywood manufacture the veneer is rotary peeled. It is used because of its lower cost and higher yield. However, sliced veneer can be produced by a ‘slicer’, the strips of veneer being cut in a straight line action. Sliced veneers are generally used for decorative faces to highlight the natural timber grain pattern or ‘figure’. This pattern can be varied depending on the angle of the slice through the log.
Plywood Fabrication Lay-up : The dried, graded veneers are usually assembled in two bundles in preparation for the spreading operation. In one bundle the graded faces and long bands are assembled and the other consists of the crossbands or in the case of three ply, the cores. It is these crossbands or cores which are run through the glue spreader. Different grades of plywood are made from various grades of faces, backs, crossbands and cores. In a three ply construction only the centre veneer passes through the glue spreader. The glue is transferred to the adjacent veneers in the pressing operations.
Glue Mixing : The adhesives currently used for plywood manufacture are based on synthetic resins and are all thermo-setting, i.e. they are cured by heat and are not replasticised by subsequent heating. The adhesives have a defined series of bond tests and are grouped as shown below on the basis of their durability.
|A Bond||Phenol, Resorcinol or Tannin|
|Fully weather resistant|
|B Bond||Melamine fortified Urea|
|Partially weather resistant (2-5 years|
|C Bond||Urea Formaldehyde||Interior glue - high humidity applications|
|D Bond||Extended Urea formaldehyde||Interior glue - low humidity|